1. Technical Field
The disclosure relates to cavity filters, and more particularly relates to a tuning structure of a cavity filter.
2. Description of Related Art
Cavity filters are popularly applied in mobile communications. FIG. 3 is a cross-sectional view of a commonly used cavity filter 10. The cavity filter 10 comprises a bottom portion 16 and one or more sidewalls 11 extending from edges of the bottom portion 16, which collectively define a cavity 100 with an opening on a top portion opposite to the bottom portion 16. A plurality of resonators 13 are secured on the bottom portion 16, each defining a resonating body 131 in communication with the cavity 100. A lid 12 covers the opening of the cavity 100 and comprises a plurality of bases 14 each extending from the lid 12 toward one resonator 13. A plurality of threaded holes 141 penetrate the lid 12 and one of the bases 14 facing the resonating bodies 131 of the resonators 13, respectively. Each threaded hole 141 corresponds to and receives a tuning post 15 providing adjustment of a resonating frequency of the cavity filter 10.
However, during adjustment of the resonating frequency of the cavity filter 10, metal shavings may be produced by the tuning posts 15, because the tuning posts 15 and the lid 12 are both metal. Such shavings can migrate to electronically sensitive areas of the cavity 100, with resulting intermodulation distortion (IMD) of the cavity filter 10.
Therefore, a need exists in the industry to overcome the described limitations.